Such is Kepler's explanation of the Star of Bethlehem. But before he had given this to the world, indeed while he was an infant in his cradle, Tycho Brahe had connected the phenomenon with that of one of the great variable stars of the solar system.
The latter astronomer discovered, in 1572, what appeared to be a new star in the constellation, Cassiopeia. It was a star of the first magnitude when first perceived, and daily it increased in brilliancy, till it out-shone Sirius, equaled Venus in lustre, and could be perceived, even by the naked eye, at noonday. For nearly a month the star shone; at first it had a white light, then a yellow, and finally it was a bright red. Then it slowly faded, and in about sixteen months had disappeared.
Amidst all the conjecture concerning this remarkable appearance, some regarding it as a new world in process of creation, others as a sun on fire, Tycho Brahe held to the belief, though unable to prove it, that it was a star with a regular period of light and of darkness, caused possibly by its nearness to, or distance from, the earth. When the telescope was invented, forty years later, the accuracy of this theory was known. At the spot carefully mapped out by Tycho Brahe, a telescopic star was found, undoubtedly the same one whose brilliant appearance had so startled the world in 1572. Upon this, astronomers began to study the annals of their science for similar appearances, and found that a very brilliant star had appeared and disappeared near the same spot in the heavens in 1264, and also in 945. The inference was that this star had a period of about three hundred years, and counting back, imagination might place one of its periods of brilliancy very near the time of Christ's birth. For this reason it received the name of the Star of Bethlehem, and many have fully accepted the theory which makes this variable luminary identical with the "Star of the East."
This second theory has especial interest just now, for if astronomical calculations are correct, we may look for the reappearance of this remarkable star during the coming year. If it does fulfill the prediction of its return it must be reckoned as one of the most noteworthy phenomena of the century.
For the benefit of amateur observers, who are as likely as any to be the first to perceive this remarkable sight, we may say that Cassiopeia, the constellation in which it will appear, lies very near the North Star. You all know how to find the Polar Star by the pointers of the Great Dipper; continue this line beyond about an equal distance, and you will strike Caph, the largest star in Cassiopeia, or the Chair, so-called because the stars form the outline of an inverted chair. Near one of these the wandering luminary will probably flash out, "to amaze a wondering world."
We may remark, in conclusion, that though there are quite a number of variable stars, their nature and the cause of their changes are but imperfectly understood. The Star of Bethlehem has no doubt an orbit, which brings it much nearer the earth at some times than others. But astronomers do not believe that the mere fact of distance explains all changes. There is a star known as Mira, which for eleven months is wholly invisible to the naked eye, then flames forth as a star of the first magnitude, and is visible for a period of nearly three months, fading at its close into darkness again. The star Algol, in the constellation Perseus, is usually of the second magnitude, but every two and a-half days it begins to decline in brilliancy, becomes very faint, and remains thus for about three hours, and then waxes bright again. Possibly this may be caused by the shadow of another star. In 1866 a star of the eighth magnitude, in the Northern Crown, suddenly flamed up into extraordinary brilliancy, remained thus for several months and gradually subsided. This star was examined with the spectrum, and showed lines of burning hydrogen. This led to the theory, now held, that the increase in brilliancy of these stars is caused by the incandescence of this gas. These fixed stars are all supposed to be suns of other systems, and to be surrounded—like our sun—with envelopes of fiery gases; from some cause not at all understood these gases may, at regular periods, flame up with fiercer heat than usual, and produce this appearance of greatly increased light. This is a very inadequate explanation, no doubt, but it is the best that astronomers have yet been able to devise in the matter.
A.C.C.